This invention relates to a lead frame workholder and transport apparatus for holding and moving a strip of semiconductor lead frames from an inlet station to an application station as in a die bonder for bonding dies or chips to lead frames in the field of semiconductor devices, and more particularly concerns a lead frame workholder for holding and transporting a strip of lead frames from a stack in an inlet station to an epoxy station for applying a layer of epoxy to the pads of the lead frames and for transporting the epoxied lead frames to a die bonding station for applying a die to the epoxy layer. The invention also includes a method of using the apparatus.
A lead frame is a stamped metal frame having leads extending inwardly and outwardly from a frame and having a central pad on which an integrated circuit chip or die is mounted and used in the semiconductor industry. There are many different sizes of lead frames with different widths, different lengths, and different numbers of leads extending from the frame. To mount a die on the pad of a lead frame, a workholder is used to hold a strip of lead frames, typically with five or eight mounting pads, but it can have any number, while it is being transported from an input station to an epoxy station where an epoxy layer is applied to the pad of each lead frame, and to a die bonding station where a die is applied to each adhesive layer to form a die bonded lead frame which is later processed into a desired integrated circuit package.
Referring to FIG. 1, which is illustrative of a conventional lead frame workholder, there is shown a workholder 11 which has a lead frame input carrier 13 that holds a stack of lead frame strips 15 each of which includes a number of lead frames 17, with this particular lead frame strip 15 showing 10 lead frames 17.
Each lead frame 17 has a centrally located bond or die pad 19 on which a die is to be mounted, and each lead frame 17 also has a locating pin hole 21 which is used to locate the lead frame 17 in the correct position at the epoxy and bond stations.
The distance between adjacent die pads 19 is referred to as the pitch between pads, and the pitch may be measured from the center line of one pad to the center line of the adjacent pad.
Input carrier 13 is provided with a lead frame separator 23 which separates the lead frame strips 15 in the stack.
Each lead frame strip 15 is fed separately through feed pinch rollers 25 along a track 27 to a clamp bar 29 and alignment pin 31 at the epoxy station 33 where an epoxy layer is applied to each die pad 19.
The epoxied lead frame strip 15 is then moved forwardly by pinch rolls 35 to a die bonding station 37 where a die or chip is attached to the epoxy layer.
Exit pinch feed rollers 39 move the die bonded lead frame strip 15 out of the machine and into an exit carrier.
During the passage of the lead frame strip 15 through the machine, it is guided by lead frame groove 41 in the far side wall of the track 27.
Conventional workholder 11 has a number of problems. The pinch rollers 25, 35, 39 may bend the lead frame strips 15 which are rather delicately constructed and must maintain their flatness in order to avoid problems in further assembly and packaging steps.
Also, in resetting the conventional workholder 11 for lead frame strips of another size, a great number of parts must be removed and replaced by parts which fit the size of the ne lead frame strip. The production down time while making this changeover is substantial, and can cost a great deal of money. The longer the down time the less production there is and the bigger the cost. If there must be a changeover four times a day, the cost of the down time becomes very significant.